1. Field of the Invention
The present invention relates to a fuel cell system running on high pressure gas.
2. Description of the Related Art
A typical fuel cell system running on high pressure gas is equipped with a high pressure tank in which an isolation valve is installed, and this isolation valve is an in-tank electromagnetic valve. Such an isolation valve is positioned upstream of a regulator for depressurizing the high pressure gas. Furthermore, the valve is opened during the operation of the system, and is closed during the stop of the system. In this way, the supply of the fuel is blocked during the stop. In addition, if there should be any trouble in a device of the system, such as a regulator, positioned downstream of the isolation valve, the fuel could not flow out thereto. An example of an isolation valve of this type is described in Japanese Examined Patent Application Publication H7-18384.
However, the exemplified isolation valve has the following disadvantage. Assume that a system equipped with this isolation valve operates at a temperature nearly equal to the lower limit of its own guaranteed temperature range. If this system is connected to a heavy load, it consumes the high pressure gas rapidly. As a result, the temperature of the gas in the high pressure tank may drop below the lower limit of the guaranteed temperature range, because the isoentropic expansion occurs in the tank. This possibly causes the degradation of blocking property of the isolation valve, especially the property of seal section of the isolation valve.
Taking the above disadvantage into account, the present invention has been conceived. An object of the present invention is to provide a fuel cell system that has a function of preventing the degradation of all devices including a high pressure tank and a fuel cell, upon operation at low temperatures.